Tube tester for a Predicta 21EAP4 - Videokarma.org TV - Video

rickfray · #1 02-21-2013, 09:31 PM

I have a Predicta Holiday I'm starting to restore with a 21EAP4 tube. I wanted to test the tube to see if it was any good before attempting an electronic overhaul. I got a B&K 465 CRT tester off ebay but didn't realize until I got it that it didn't have any adapters except the color one with the molex connector. The schematic with the B&K shows an "A" adapter that I suppose corresponds to the tube setup chart for 21EAP4 which says use adpater "A". The problem is, the schematic just shows a standard round 8 pin socket symbol with 6 of the pins wired but the tube connector is an oddball 5 pin with 5 wires (2 up, 1 in the middle, 2 down-slightly wider than the top 2) so I can't confirm that is actually the right adapter. I've seen some other 465's on ebay with inconclusive pictures of adapters to assure me the they will work with an EAP4.

Has anyone actually tested a 21EAP4 with a B&K 465 and can confirm what adpater I need, or how to build one? I do have the color adapter that connects to the universal B&K plug/cable that has the molex connector on the end, so I'm guessing if I can confirm the correct tube pinout to use, I could get a molex and make at least a jumper cable adapter.

Also I'd appreciate a copy of a tube manual page for the 21EAP4 if anyone can scan it. I have a few tube manuals but not for the 21EAP4. Many thanks as I start on my Holiday fixer upper.

Rick

***Eric H*** · #2 02-21-2013, 09:56 PM

Hi Rick, welcome to VK.

The 465 should be able to test that tube, with the color adapter removed the socket on the 465 will fit the older B&W tubes like the 10BP4 so you could use the diagram of that tube to figure out the pinout of the tester and apply it to the Predicta tube.

I know the 465 uses a specific Cutoff voltage for different tubes, I have a 466 and the settings for 95% of the B&W tubes are the same but it does not work the same way as the 465, it also has an A & B socket, possibly the same adapter as used by the 465.
Someone here is bound to have a 465 and will be able to tell you what settings to use.

I would caution that tube has an odd heater voltage of 2.35 volts so if you do get it hooked up be sure the voltage is set right first.

Collectively our experiences here with the original Predicta tubes is that they are more often bad than not, hopefully yours will be the exception.

marty59 · #3 02-22-2013, 08:21 AM

Here's tube data for you courtesy of Bunker of Doom

http://www.bunkerofdoom.com/tubes/syl59/HTMLS/CRT.HTM

rickfray · #4 02-22-2013, 07:09 PM

Many thanks for the tube data marty59!

Rick

rickfray · #5 02-22-2013, 07:13 PM

Eric, It's not the settings I'm worried about, it's whether I can find the right adapter. The socket connected to the 465 via the cable has 12 pins, but the 21EAP4 only has 5 pins on a 5/8" round plug and they aren't in a circle like most of the adapters I've seen. If I could see a picture of the "A" socket holes, I'd know for certain if that's the one.

As an alternative option, what CRT testers have Predicta restorers used to test a 21EAP4? Thanks

Rick

marty59 · #6 02-22-2013, 09:15 PM

Quote:

Originally Posted by rickfray

Eric, It's not the settings I'm worried about, it's whether I can find the right adapter. The socket connected to the 465 via the cable has 12 pins, but the 21EAP4 only has 5 pins on a 5/8" round plug and they aren't in a circle like most of the adapters I've seen. If I could see a picture of the "A" socket holes, I'd know for certain if that's the one.

As an alternative option, what CRT testers have Predicta restorers used to test a 21EAP4? Thanks

Rick

You can "test" with just about any tester, rejuvinating opinions/options will vary and that Predicta tube is delicate.

Like tube testers, you can't have just one!

***Eric H*** · #7 02-23-2013, 12:29 AM

Here are some pictures of the A & B sockets from my 466, it's probably the same as the one for the 465 since the 12 pin socket is the same, I don't remember which one is used for the 21EAP4 off hand but I can look it up.

Even though there are 12 pins in the tester socket I believe only 5 of them are used, 2 for the heater, G1, G2, and Cathode (K).

In any case I wouldn't rejuvenate a Predicta CRT (or much else) with a 465 or a 466, they are just brute force blasting, probably a 470 is the earliest B&K with a decent rejuvenation system.
They are fine for testing though.

radiotvnut · #8 02-23-2013, 12:46 AM

I agree about the 465. 20+ years ago, my first CRT tester was a 465 that was given to me by a repair shop who no longer used it. It was fine for testing; but, wasn't as fine for rejuvenating. I was able to bring quite a few standard B&W tubes back to life by popping them on the lowest setting (which, is still harsh); but, I also blew up quite a few tubes in an attempt to rejuvenate them. Within a few years, I bought a B&K 470 and I don't recall ever smoking a tube with it's rejuvenate function. I've had some CRT's that were simply too worn out to rejuvenate; but, I don't recall one ever being ruined.

Once, I loaned my 465 to someone who wanted to rejuvenate a color tube. Despite my warning, he thought that starting out on the highest setting would do the best good. Well, it did the best good at ruining his tube. Those models have three levels of rejuvenation for a reason and one is supposed to try the lowest setting first. If that works, don't go any further.

The B&K 467 and later model numbered units have safe rejuvenate functions, as does the Sencore CR70 and newer units.

When I rejuvenate a tube with my 470, I always start with the "clean and balance" function. This is a lower level of rejuvenation and is often all that's needed to bring a tube back.

kx250rider · #9 02-23-2013, 12:04 PM

I think there are a couple of wires swapped for the Predicta tubes, to prevent the filaments from coming on if somebody puts a 2.7 volt tube in a 6.3 volt TV, or from installing a 6.3 volt tube in a Predicta. If you don't have the right socket, you can check the schematics of the Predicta and any other TV with that size socket but standard filaments, and temporarily swap the wires.

Charles

***Eric H*** · #10 02-23-2013, 12:52 PM

Quote:

Originally Posted by kx250rider

I think there are a couple of wires swapped for the Predicta tubes, to prevent the filaments from coming on if somebody puts a 2.7 volt tube in a 6.3 volt TV, or from installing a 6.3 volt tube in a Predicta. If you don't have the right socket, you can check the schematics of the Predicta and any other TV with that size socket but standard filaments, and temporarily swap the wires.

Charles

There's a difference but it's not the heaters, I think they swapped G1 and K or similar. Using the wrong socket just results in the meter pegging.

rickfray · #11 02-23-2013, 09:32 PM

Thanks for the pictures Eric, but the brightness makes it hard to tell. The BK 465 setup guide sais the 21EAP4 should use the "A" socket, but the your "socka" pic doesn't look like the plug. There needs to be a pin hole in the middle of 4 other pins. The schematic for adapter "A" shows an 8 pin socket but only 6 holes are wired up so that's confusing also. I'm adding pictures below of the actual tube connector and jack on the circuit board. The plug is about 5/8" in diameter.

bandersen · #12 02-23-2013, 10:34 PM

You tester plugs right into the CRT base not that cable.

***Eric H*** · #13 02-24-2013, 02:01 AM

Bobs correct, you plug the adapter directly onto the base of the CRT, after removing the connector that's plugged onto it.

The plug you show is just the plug in cable they used so the head could be removed from the body of the set.

charokeeroad · #14 02-24-2013, 10:50 AM

I may be able to help. I've tested several 21" Predicta tubes in the last few weeks with a B&K 465. It will take me an hour or so to put all the pieces together but I think it will give you the info your looking for. I'll post pieces at a time so here goes. First, two pictures of the adapter. The heater pins on the adapter are marked on the adapter as 1 and 2 but I think it's better described as the sockets on each side of the key. These pins are the same for the 2.3V CRT and the 6V CRT. My set up data doesn't call out any differences in the wiring between the 6V and the 2.3volt.

On my adapter you can see that I cut into the black lead which is one of the heater leads and added some wire and some clips. I use these clips to do a current measurement as I'm testing the CRT.

charokeeroad · #15 02-24-2013, 11:03 AM

Here is a copy of an email from Tom Albrecht who helped me resolve the 2.3v CRT vs the 6v CRT delema. Often it's not possible to tell the difference between the two even when the CRTs are marked with one or the other designations. Only a current test can tell them apart. I found a few sets clearly marked with "21SFA" inside the plastic housing which is not a correct description of any CRT the closest is SF21A which is a 6.3v CRT. After testing the current in these CRT they were found to be good 6v CRTs.

"From: Tom and Catherine Albrecht
To: Cherokeeroad
Sent: Monday, February 11, 2013 10:33 PM
Subject: Re: 21SFA

John,

I studied the schematic and confirmed that the original SF-21A CRT has a 600 mA filament current (same as all standard 6 volt CRTs). That would seem to suggest that both of the tubes you are looking at are 6 volt tubes. At some point if you disassemble the plastic CRT housing, I bet you'll find a number on the tube for a standard 6 volt tube.

If you find a CRT that draws 600 mA at 2.34 volts, then that is an original CRT with 2.34 V filament. At 6 volts it would draw substantially more. A 6 volt tube will draw less than 600 mA at 2.34 volts.
By the way, while they are warming up, they draw quite a bit more. They settle into their nominal value once the filament is hot.

Tom"

Hope this helps.